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            <div><h4 class="title">
                <a name="asio.reference.basic_random_access_file.async_read_some_at"></a><a class="link"
                                                                                            href="async_read_some_at.html"
                                                                                            title="basic_random_access_file::async_read_some_at">basic_random_access_file::async_read_some_at</a>
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    <p>
        <a class="indexterm" name="asio.indexterm.basic_random_access_file.async_read_some_at"></a>
        Start
        an asynchronous read at the specified offset.
    </p>
    <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
    <span class="keyword">typename</span> <a class="link" href="../MutableBufferSequence.html"
                                             title="Mutable buffer sequence requirements">MutableBufferSequence</a><span
                class="special">,</span>
    <span class="keyword">typename</span> <a class="link" href="../ReadToken.html" title="Read token requirements">ReadToken</a> <span
                class="special">=</span> <a class="link"
                                            href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span
                class="emphasis"><em>DEFAULT</em></span></a><span class="special">&gt;</span>
<a class="link"
   href="../asynchronous_operations.html#asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span
        class="emphasis"><em>DEDUCED</em></span></a> <span class="identifier">async_read_some_at</span><span
                class="special">(</span>
    <span class="identifier">uint64_t</span> <span class="identifier">offset</span><span class="special">,</span>
    <span class="keyword">const</span> <span class="identifier">MutableBufferSequence</span> <span
                class="special">&amp;</span> <span class="identifier">buffers</span><span class="special">,</span>
    <span class="identifier">ReadToken</span> <span class="special">&amp;&amp;</span> <span
                class="identifier">token</span> <span class="special">=</span> <a class="link"
                                                                                  href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span
                class="emphasis"><em>DEFAULT</em></span></a><span class="special">);</span>
</pre>
    <p>
        This function is used to asynchronously read data from the random-access
        handle. It is an initiating function for an <a class="link" href="../../overview/model/async_ops.html"
                                                       title="Asynchronous Operations">asynchronous
        operation</a>, and always returns immediately.
    </p>
    <h6>
        <a name="asio.reference.basic_random_access_file.async_read_some_at.h0"></a>
        <span><a name="asio.reference.basic_random_access_file.async_read_some_at.parameters"></a></span><a class="link"
                                                                                                            href="async_read_some_at.html#asio.reference.basic_random_access_file.async_read_some_at.parameters">Parameters</a>
    </h6>
    <div class="variablelist">
        <p class="title"><b></b></p>
        <dl>
            <dt><span class="term">offset</span></dt>
            <dd><p>
                The offset at which the data will be read.
            </p></dd>
            <dt><span class="term">buffers</span></dt>
            <dd><p>
                One or more buffers into which the data will be read. Although the
                buffers object may be copied as necessary, ownership of the underlying
                memory blocks is retained by the caller, which must guarantee that
                they remain valid until the completion handler is called.
            </p></dd>
            <dt><span class="term">token</span></dt>
            <dd>
                <p>
                    The <a class="link" href="../../overview/model/completion_tokens.html" title="Completion Tokens">completion
                    token</a> that will be used to produce a completion handler, which
                    will be called when the read completes. Potential completion tokens
                    include <a class="link" href="../use_future.html" title="use_future"><code
                        class="computeroutput"><span class="identifier">use_future</span></code></a>,
                    <a class="link" href="../use_awaitable.html" title="use_awaitable"><code
                            class="computeroutput"><span class="identifier">use_awaitable</span></code></a>,
                    <a class="link" href="../yield_context.html" title="yield_context"><code
                            class="computeroutput"><span class="identifier">yield_context</span></code></a>,
                    or a function object with the correct completion signature. The function
                    signature of the completion handler must be:
                </p>
                <pre class="programlisting"><span class="keyword">void</span> <span
                        class="identifier">handler</span><span class="special">(</span>
  <span class="keyword">const</span> <span class="identifier">asio</span><span class="special">::</span><span
                            class="identifier">error_code</span><span class="special">&amp;</span> <span
                            class="identifier">error</span><span class="special">,</span> <span class="comment">// Result of operation.</span>
  <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span
                            class="identifier">bytes_transferred</span> <span
                            class="comment">// Number of bytes read.</span>
<span class="special">);</span>
</pre>
                <p>
                    Regardless of whether the asynchronous operation completes immediately
                    or not, the completion handler will not be invoked from within this
                    function. On immediate completion, invocation of the handler will
                    be performed in a manner equivalent to using <a class="link" href="../post.html" title="post"><code
                        class="computeroutput"><span class="identifier">post</span></code></a>.
                </p>
            </dd>
        </dl>
    </div>
    <h6>
        <a name="asio.reference.basic_random_access_file.async_read_some_at.h1"></a>
        <span><a name="asio.reference.basic_random_access_file.async_read_some_at.completion_signature"></a></span><a
            class="link"
            href="async_read_some_at.html#asio.reference.basic_random_access_file.async_read_some_at.completion_signature">Completion
        Signature</a>
    </h6>
    <pre class="programlisting"><span class="keyword">void</span><span class="special">(</span><span class="identifier">asio</span><span
            class="special">::</span><span class="identifier">error_code</span><span class="special">,</span> <span
            class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span><span
            class="special">)</span>
</pre>
    <h6>
        <a name="asio.reference.basic_random_access_file.async_read_some_at.h2"></a>
        <span><a name="asio.reference.basic_random_access_file.async_read_some_at.remarks"></a></span><a class="link"
                                                                                                         href="async_read_some_at.html#asio.reference.basic_random_access_file.async_read_some_at.remarks">Remarks</a>
    </h6>
    <p>
        The read operation may not read all of the requested number of bytes. Consider
        using the <a class="link" href="../async_read_at.html" title="async_read_at"><code class="computeroutput"><span
            class="identifier">async_read_at</span></code></a>
        function if you need to ensure that the requested amount of data is read
        before the asynchronous operation completes.
    </p>
    <h6>
        <a name="asio.reference.basic_random_access_file.async_read_some_at.h3"></a>
        <span><a name="asio.reference.basic_random_access_file.async_read_some_at.example"></a></span><a class="link"
                                                                                                         href="async_read_some_at.html#asio.reference.basic_random_access_file.async_read_some_at.example">Example</a>
    </h6>
    <p>
        To read into a single data buffer use the <a class="link" href="../buffer.html" title="buffer"><code
            class="computeroutput"><span class="identifier">buffer</span></code></a> function as follows:
    </p>
    <pre class="programlisting"><span class="identifier">handle</span><span class="special">.</span><span
            class="identifier">async_read_some_at</span><span class="special">(</span><span
            class="number">42</span><span class="special">,</span> <span class="identifier">asio</span><span
            class="special">::</span><span class="identifier">buffer</span><span class="special">(</span><span
            class="identifier">data</span><span class="special">,</span> <span class="identifier">size</span><span
            class="special">),</span> <span class="identifier">handler</span><span class="special">);</span>
</pre>
    <p>
        See the <a class="link" href="../buffer.html" title="buffer"><code class="computeroutput"><span
            class="identifier">buffer</span></code></a>
        documentation for information on reading into multiple buffers in one go,
        and how to use it with arrays, boost::array or std::vector.
    </p>
    <h6>
        <a name="asio.reference.basic_random_access_file.async_read_some_at.h4"></a>
        <span><a
                name="asio.reference.basic_random_access_file.async_read_some_at.per_operation_cancellation"></a></span><a
            class="link"
            href="async_read_some_at.html#asio.reference.basic_random_access_file.async_read_some_at.per_operation_cancellation">Per-Operation
        Cancellation</a>
    </h6>
    <p>
        This asynchronous operation supports cancellation for the following <a class="link"
                                                                               href="../cancellation_type.html"
                                                                               title="cancellation_type"><code
            class="computeroutput"><span class="identifier">cancellation_type</span></code></a>
        values:
    </p>
    <div class="itemizedlist">
        <ul class="itemizedlist" type="disc">
            <li class="listitem">
                <code class="computeroutput"><span class="identifier">cancellation_type</span><span
                        class="special">::</span><span class="identifier">terminal</span></code>
            </li>
            <li class="listitem">
                <code class="computeroutput"><span class="identifier">cancellation_type</span><span
                        class="special">::</span><span class="identifier">partial</span></code>
            </li>
            <li class="listitem">
                <code class="computeroutput"><span class="identifier">cancellation_type</span><span
                        class="special">::</span><span class="identifier">total</span></code>
            </li>
        </ul>
    </div>
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                Distributed under the Boost Software License, Version 1.0. (See accompanying
                file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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